How to use Symfony Messenger component in standalone code to send AMQP messages

This can be improved but it works for me:

use Symfony\Component\Messenger\Bridge\Amqp\Transport\AmqpSender;
use Symfony\Component\Messenger\Bridge\Amqp\Transport\Connection;
use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\MessageBus;
use Symfony\Component\Messenger\Middleware\SendMessageMiddleware;
use Symfony\Component\Messenger\Transport\Sender\SendersLocatorInterface;

$sendersLocator = new class implements SendersLocatorInterface {
    public function getSenders(Envelope $envelope): iterable
    {
        $connection = new Connection(
            [
                'hosts' => 'localhost',
                'port' => 5672,
                'vhosts' => '/',
                'login' => 'guest',
                'password' => 'guest'
            ],
            [
                'name' => 'messages'
            ],
            [
                'messages' => []
            ]
        );
        return [
            'async' => new AmqpSender($connection)
        ];
    }
};

$middleware = new SendMessageMiddleware($sendersLocator);

$bus = new MessageBus([$middleware]);

$bus->dispatch(new MyMessage());

I modified the above answer to let me pass the RabbitMQ credentials as an environment variable. This is what I needed for my application. I was trying to write my own DSN parser and discovered that Symfony already does it, so I basically lifted the code from there.

If the environment variable is not set, it defaults to use the same settings shown in the example above.

use Symfony\Component\Messenger\Bridge\Amqp\Transport\AmqpSender;
use Symfony\Component\Messenger\Bridge\Amqp\Transport\Connection;
use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\MessageBus;
use Symfony\Component\Messenger\Middleware\SendMessageMiddleware;
use Symfony\Component\Messenger\Transport\Sender\SendersLocatorInterface;

$sendersLocator = new class implements SendersLocatorInterface {
    public function getSenders(Envelope $envelope): iterable
    {
        $dsn = getenv('MESSENGER_TRANSPORT_DSN') ?: $_ENV['MESSENGER_TRANSPORT_DSN'];

        $connection = Connection::fromDsn($dsn); 

        return [
            'async' => new AmqpSender($connection)
        ];
    }
};

$middleware = new SendMessageMiddleware($sendersLocator);

$bus = new MessageBus([$middleware]);

$bus->dispatch(new MyMessage());